This invention relates generally to diagnostic and therapeutic devices for implant in a patient's body, and more particularly to devices that monitor physiologic parameters and/or provide corrective therapies in conjunction with external monitoring and/or programming devices.
A wide variety of implantable devices have been developed for use in the human body to monitor the patient's condition and/or to treat a patients underlying disease state. Of these, implantable pacemakers are probably the most widely known, but also available are implantable defibrillators, implantable drug delivery devices, implantable nerve and muscle stimulators and a variety of implantable monitors. Most of these devices are used in conjunction with external monitoring and/or programming devices that control the operation of the implanted devices and receive information from the implantable devices. Examples of programmable implantable pacemakers include U.S. Pat. No. 5,456,692, issued to Smith et al., U.S. Pat. No. 5,843,138, issued to Evers, U.S. Pat. No. 5,372,607, issued to Stone et al., U.S. Pat. No. 5,843,139, issued to Goedeke et al., U.S. Pat. No. 4,601,291, issued to Boute et al., U.S. Pat. No. 5,693,076, issued to Kaemmerer, et al., U.S. Pat. No. 5,752,977, issued to Grevious et al., U.S. Pat. No. 5,354,319 issued to Wyborny et al. and U.S. Pat. No. 5,107,833, issued to Barsness et al., all incorporated herein in their entireties. Examples of the various other types of programmable implantable devices listed above include U.S. Pat. No. 5,342,408, issued to DeCoriolis et al., U.S. Pat. No. 5,383,909, issued to Keimel, U.S. Pat. No. 4,146,029, issued to Ellinwood, U.S. Pat. No. 4,692,147, issued to Dugan, U.S. Pat. No. 5,662,689, issued to Ellsberry et al, U.S. Pat. No. 5,342,409, issued to Mullett and U.S. Pat. No. 5,331,966, issued to Bennett et al., all incorporated herein in their entireties.
In many of the devices described above, activation of telemetry from the implanted device to the associated external device requires placement of a magnet in physical proximity to the device. The same type of magnet may also activate a temporary change in device operation. The best-known example of such an operational mode change is the initiation of asynchronous pacing operation in an implantable pacemaker, enabling the patient or the patient's physician to conveniently determine the present pacing rate. This type of magnetically triggered mode change is also useful in the context of trans-telephonic pacemaker monitoring, allowing the remote monitoring device to record a paced electrogram, if desired.
The requirement of magnetic activation of the device's telemetry function or mode change, while serving as a useful safety feature, does have some drawbacks. First, the magnets employed are typically relatively heavy, high power magnets of a type not typically available other than from the device manufacturer, making them inconvenient and expensive to replace in the event they are lost or broken. This does not pose a problem in the context of programming or monitoring the implanted device using a programmer which employs a programming head placed in proximity to the patient's body, as such programming heads typically include a built-in magnet, typically a permanent magnet. However, as programming systems which employ programming antennas which may be remote from the body are developed, for example as disclosed in U.S. Pat. No. 5,113,869, issued to Nappholz et al., U.S. patent application Ser. No. 09/302,932, filed on Apr. 30, 1999 by Villaseca et al., for a "Telemetry System for Implantable Medical Devices", U.S. patent application Ser. No. 09/302,637, filed on Apr. 30, 1999 by Goedeke, for a "Telemetry System for Implantable Medical Devices", all incorporated herein in their entireties, a magnet within the programmer is not workable. Second, placement of the magnet in proper orientation and location with regard to the implanted device is sometimes difficult, making the process more cumbersome than might be desirable.